1. Field of Invention
The invention relates to a stamper forming method and, in particular, to a stamper forming method for digital audio/video (AV) optical disks.
2. Related Art
During the optical disk production process, the original digital data or signals have to be converted into laser embossing signals. After completing the embossing and electroplating processes in a clean room, a master for mass production is then produced. Afterwards, the master is used to make a stamper for subsequent production processes.
As shown in FIG. 1A, a CD-R/RW or DVD-R stamper is formed with a plurality of grooves of the same depth, H1 (about 25 nm to 30 nm), in a readable embossed area (Area A) and an unreadable embossed area (Area B). To make optical disks compatible with CD-ROM drives and to allow a normal DVD-ROM to read optical disks with the DVD-RW format, signals in the readable embossed area (Area A) are partially modified in DVD-RW Ver 1.1. More explicitly, the groove depth H2 of the readable embossed area (Area A) is increased to 100 nm, as shown in FIG. 1B, for enhancing the signal reading mode.
However, in current manufacturing processes, laser beams of different strengths are used to directly etch desired groove depths (H1 and H2) on positive photoresist 3 in the stamper (FIG. 1B). As energy dispersion in photoresist is difficult to control, using a laser beam with a fixed intensity may still result in grooves with an error of depth between 2 nm and 3 nm. The precision of the groove depth is therefore difficult to control. Moreover, there may be problems of poor homogeneity and different geometries in the grooves with the depths (H1 and H2), as shown in FIG. 1C. The above-mentioned problems are not good for optical signal reading.
In view of the foregoing problems, the inventor provides a stamper forming method that has been implemented in the laboratory to solve the problems.
It is an objective of the invention to provide a stamper forming method with high precision, simple controls, improved homogeneity, and standard geometrical shapes for the grooves.
To achieve the above objective, the invention provides a stamper forming method including the following steps: coating a first photoresist on a substrate, coating a stop layer on the first photoresist, coating a second photoresist on the stop layer, exposing the second photoresist by using a beam of light, exposing the first photoresist by using another beam of light, developing the first photoresist and the second photoresist, and sputtering a metal layer. Moreover, the invention also provides another stamper forming method including the following steps: coating a first photoresist on a substrate, coating a first stop layer on the first photoresist, coating a second photoresist on the first stop layer, coating a second stop layer on the second photoresist, coating a third photoresist on the second stop layer, exposing the third photoresist by using a beam of light, exposing the second photoresist by using another beam of light, exposing the first photoresist by using yet another beam of light, developing the first, second, and third photoresists, and sputtering a metal layer in the direction of the third photoresist.
The stamper forming method of the invention improves the geometrical shape of the grooves to meet the desired standards by changing the number of photoresist and inserting stop layers between the photoresists. In comparison with the prior art, the depth of the grooves can be readily and precisely controlled in the disclosed multilayer photoresist structure. Adjusting the number of photoresist layers can form grooves of different depths. Since there are problems due to the difficulty in controlling energy dispersion in the photoresist, the homogeneity and geometry of the grooves therefore have a higher level of precision, which is good for optical signal reading. The yield of the stamper also increases at the same time. In view of the above-mentioned advantages, the disclosed stamper forming method is very useful in the industry.